Micro CHP (Combined Heat & Power)
replaces the gas boiler in a central heating system.It burns gas to produce space & water heating,
whilst simultaneously generating around 3000kWh of
electricity annually.Effectively each unit of electricity “costs” a
unit of heat that would otherwise have been produced in
the boiler, saving money and carbon.

?

Pro

Generates
significant amounts of low carbon electricity

Cost
effective energy efficiency device

Con

Current
technology suited only to larger homes

Verdict

The single most
cost-effective energy efficiency and carbon mitigation
technology for housing

Micro CHP is defined by
the UK Government as being CHP with an electrical output less than
50kWe; this clearly includes units far too big for individual homes
for which products up to 3kWe and normally around the 1kWe level are
most common. This section deals only with domestic micro CHP,
suitable for individual family homes;
products from 5-50kWe are dealt with under
mini CHP.

There
are a number of micro CHP technologies, each of which offers
benefits in different applications. They are normally
categorised by the "prime mover", that is the engine or other device
which produces heat and power from the input fuel.
Technologies currently in use or approaching market readiness
include engines (Stirling, Rankine and Internal Combustion), which
burn fuel in the engine to drive a generator and produce heat, and
fuel cells which convert gas directly into heat and electricity
through an electro-chemical process.

The economics of micro CHP depend primarily on the
generation of electricity; electricity is significantly more
valuable than heat both in economic and carbon terms. Thus, in
order to maximise the value of this generation, it is desirable to
run the system for as many hours per year as possible, so that
products with high electrical efficiency (and relatively low heat
output) are desirable. However, it is also important that the
cost of the product does not result in extended payback periods;
typically around 3-5 years is considered viable and micro CHP is
unique amongst microgeneration technologies in being able to achieve
paybacks this short.

The principal challenge for any micro CHP
technology is to operate for sufficient hours to recover the
investment. Target life for micro CHP is around 30,000 hours,
representing 10 years operation in a typical family home. This
is an extremely onerous challenge and is the main technical obstacle
to most products. Bear in mind that a normal car engine
requires a service every 200 hours or so and is unlikely to last
more than 2,000-3,000 hours in total!